The present invention relates to a high voltage disconnect switch, particularly a single pole disconnect switch, which includes primary movable contact pieces, a countercontact piece connected to a high voltage line, and resilient pre-contact pieces connected to the countercontact piece, wherein the pre-contact pieces are arranged to close before the closing of the primary contact pieces during switch closihg and to open before the opening of the primary contact pieces during switch opening.
The contact system of a disconnect switch is generally designed to be switched on and off only in the idle stage, that is, without the presence of a current load. For this reason no measures are generally taken in connection with disconnect switches to increase their turn-on capability or permit the disconnection of load or short-circuit currents.
In certain cases, however, a disconnect switch must be able to have a certain opening and closing capability. Such a case arises, for example, when the switch is used to connect and disconnect a high voltage long line.
If such a switch is also used to connect and disconnect a bus bar section which is connected in parallel with a second current-carrying bus bar section, an electric switching arc may develop during the opening movement of the disconnect contacts.
In known disconnect switches not equipped with special devices to increase their switching capability, the generated switching sparks may damage the contact surfaces. Over the course of time, this reduces the permanent current carrying capability of the switch. Depending on the current load, the aggressivity of the atmosphere and the duration of the influences, damaged contact points may take on such a high transfer resistance that finally the contact pieces may burn out and cause operating malfunctions.
To overcome these drawbacks, German Offenlegungsschrift Pat. No. 2,809,499 discloses equipping the primary contact pieces of a disconnect switch with resilient pre-contact pieces which during the closing of the switch close before the primary contact pieces and during the opening of the switch open after the primary contact pieces so that opening and closing of the primary contact pieces takes place without current. The contact surfaces of the primary contact pieces thus remain protected against the effects of switching arcs.
It has been found, however, that switching arcs damage the contact surface at the point of contact between the pre-contact and primary contact pieces, thus impeding current transfer and shortening the service life of the pre-contact pieces.